you are almost there, split the numerator into two and then simplify:\[\frac{\cos(x+y)}{\cos(x)\sin(y)}=\frac{\cos(x)\cos(y)-\sin(x)\sin(y)}{\cos(x)\sin(y)}=\frac{\cos(x)\cos(y)}{\cos(x)\sin(y)}-\frac{\sin(x)\sin(y)}{\cos(x)\sin(y)}\]